Embodiments in accordance with the present invention relate to a media drive apparatus and a control circuit for a media drive apparatus. In particular, embodiments in accordance with the present invention relate to a technique to store a multi-bit data corresponding to signals read from a medium before converting it to a single bit data as a recorded data.
Medium drive apparatuses using various medium such as an optical disk, a magnetic tape, and a flexible magnetic disk are known in the art. In particular, a hard disk drive (HDD) has been widely used as a storage device of a computer. The HDD is one of indispensable storage devices for current computer systems. The HDD has found widespread application such as a removable memory used in a moving image recording/reproducing apparatus, a car navigation system, a cell phone, or a digital camera, in addition to the computer, due to its outstanding characteristics.
A magnetic disk in the HDD has plural concentric data tracks, each of which records plural servo data including address information and plural data sectors. A head element accesses to a desired data sector based on address information of the servo data, making it possible to write/read data to/from the data sector.
An AD converter in a channel circuit converts analog signals from the head element to multi-bit data. The multi-bit data from the AD converter are processed by a digital FIR filter and then converted to single bit data by a decoder. The single bit data are the data recorded on the magnetic disk.
It has been previously known to hold the output of the AD converter in the channel circuit and use it for an error recovery process or circuit design of a HDD. For example, Japanese Unexamined Patent Application Publication No. 2000-105901 discloses use of multi-bit data stored in a memory in a retry process for a read error. Specifically, waveform samples from an AD converter operation are stored in a memory in a channel circuit. If an ECC process is not capable of correcting user data, the HDD obtains the waveform data stored in the memory in the channel circuit and retry the subsequent process of read data.
Use of waveform data of one sector as disclosed in the above prior art document enables to re-decode the read data without accessing to the data on the magnetic disk. The technique of the above prior art reference, however, has some possible disadvantages. For one thing, the memory in the channel circuit dedicated to storing the AD converter output values increases the circuit area.
The technique of the prior art reference also has an issue regarding the transmission speed. In a typical HDD, the data transfer rate in the channel circuit is about 1 Gbit/s. This transfer rate is for the decoded single bit data, and the total amount of the AD converted data is a multiple of the bit number of the AD conversion. A typical bits of the AD conversion is 6-bit, therefore the transfer rate for storing the AD converted data is about 6 Gbit/s. A high performance memory may be necessary to store data of such a high transfer rate, resulting in higher demands on the circuit performance and higher cost.